In a variety of minimally invasive procedures, it is desirable to remove a delivery catheter, cannula, or other delivery device while leaving in place another apparatus that has been delivered through the lumen of the delivery device. For example, a pacing lead may be delivered to a chamber or vessel of the heart through a pre-shaped or steerable delivery catheter. Subsequently, the lead is left in place while the delivery catheter is removed. In the event that the proximal end of the lead is larger than its distal end, and larger than the inner diameter of the delivery catheter, the delivery catheter must be removed by splitting, cutting, slitting, or otherwise interrupting its circumference such that the lead can exit the catheter when the catheter is withdrawn from the body.
In many cases, this removal step can be difficult. In particular, if performed incorrectly by the operator, it can result in dislodgement of the implanted lead, making therapy ineffective or requiring that the procedure be repeated in order to re-implant the lead. Lead dislodgement is one of the most frustrating and clinically problematic outcomes encountered in lead delivery. When the lead is dislodged, a procedure, which may have taken hours to get to the point of slitting, must in many cases be restarted essentially from the beginning.
One such mechanism of dislodgment that commonly occurs with currently marketed slittable catheters is “spiral slitting,” meaning that the slitting or cutting action cannot be sufficiently controlled by the physician to maintain a straight line of cutting (i.e., in a single line substantially parallel to the central axis of the catheter being slit). Instead, the line of slitting propagates at least partially in a non-linear (e.g., helical) path of variable direction and/or pitch.
The degree of spiral slitting may depend on a variety of factors, including how the operator holds the slitter relative to the delivery catheter. However, in the context of the procedure, its technical difficulty, and the many demands on the physician's attention, spiral slitting continues to be a widespread and contributory to the incidence of lead dislodgment.
Because the slitter is held in the physician's hand, it is substantially rotationally fixed, such that the consequence of spiral slitting is that the portion of the catheter distal to the slitter must inevitably rotates in sync with the direction, pitch, and speed of the slitting. This rotation, especially in the case of catheters with large shape set curves, can transfer excessive and/or irregular forces to the lead, increasing the likelihood of lead dislodgement. For example, as slitting proceeds in a non-linear path, it may cause the distal end of a pre-shaped or deflected catheter to rotate, which can both pull on the lead body and cause a significant change in path length from the percutaneous access site to the target delivery location of the lead tip. In particular, the path length may change significantly as the tip of a pre-shaped or deflected catheter rotates freely and unconstrained in an open chamber of the heart, commonly the right atrium, which occurs as the proximal portion of the delivery sheath is slit. As the delivery catheter is further withdrawn and its distal segment passes through generally narrowing vessels toward the access site, it becomes increasingly constrained, limiting the path length change caused by rotation. In any case, rotation of the delivery catheter may result in the lead tip moving from its target delivery location, i.e., becoming dislodged.
One common approach to the issue is using a peelable, rather than slittable, catheter. Peelable catheters include a natural parting line or weakened segment such that when pulled apart manually, the circumferential catheter body splits into two parts and allows the implanted device to exit. One problem with such catheters is that they generally lack a reinforcing structure such as a braid, coil, and the like, since such structures cannot be easily broken by hand. In contrast, slittable catheters generally include such a reinforcing structure, which can be cut with a sharp blade, scissors, or other cutting element. Unreinforced peelable catheters, however, suffer with respect to key performance elements, including kink resistance, torque, pushability, and tracking compared to reinforced catheters and so are generally disfavored. Further, materials such as PTFE are commonly used in peelable catheters since they can be scored and tend to propagate a tear line once initiated, however, materials with more favorable and mechanical characteristics, such as strength, resiliency, and variable Durometer (e.g., polyether block amide (PEBA), nylon, urethane, etc.), do not peel or tear as easily.
Therefore, catheters, sheaths, or other tubular devices that reduce the risk of spiral slitting or other problems would be useful.